As used herein, "ink" means any of the inks, toners or the like used by commercial printing presses, laser and impact printers, xerographic copiers or any other type of printer or copier which affixes ink, toner or the like to a cellulosic fiber substrate and wherein the ink or toner is separable from the substrate in a recycling process for recovery of the fibers.
The amount of paper and other cellulosic fiber substrates printed with electrostatic toners continues to increase as low cost laser printers and xerographic copiers become more common. As a result, electrostatic printed papers are becoming a more important fiber source for recycling mills.
Conventional ink removal processes of washing or flotation are often inadequate to the task of removing electrostatic toner ink from the fibers. The toner particles removed from the repulped fibers during conventional processes are usually flat flakes which are difficult to separate from the fiber component.
Thus, recycled papers prepared from waste papers printed with laser printers or xerographic copiers often have higher dirt counts than similar grades of recycled paper prepared from waste paper printed using other techniques. Generally speaking, as the dirt count of the recycled paper goes up, the value of the paper goes down.
Office waste is a major source of waste paper. Since businesses use a variety of printers themselves, and receive many types of printed paper, the paper received at the recycling mill often contains a variety of papers printed with a variety of inks. The inks from papers printed with more difficult to remove inks will contaminate the recycled fibers of those papers which were printed with other types of inks. For example, when papers printed with electrostatic toners are mixed with papers printed by other methods, paper prepared from the waste pulp will often have higher dirt counts than papers prepared exclusively from waste papers printed by other methods. Therefore, papers printed with inks such as electrostatic toners are not only difficult to recycle, but they may gradually contaminate the paper supply if the ink is not separated from the pulp.
The present technology for removing ink from waste paper uses one of two basic approaches. One approach is to disperse the ink particles into the pulp slurry and remove the particles from the pulp by washing and flotation technology. Washing is carried out by filtering off the fibers, while allowing the filtrate containing the ink particles to pass through the filter. Flotation is carried out by mixing air bubbles into the pulp slurry, then introducing the slurry into large flotation cells where the froth of ink and air rises to the surface, and skimming of the froth. Washing technology generates large amounts of waste water and has high losses of 10-30% of the incoming waste paper. Flotation technology is expensive, difficult to operate and has high losses of 10-15%. Operating problems with commercial flotation cells include pulp channelling, air channelling and air nozzle plugging. The pulp mass may be further processed by washing to prepare it for papermaking.
The other approach is to agglomerate the ink into particles large enough to be separated from the pulp slurry using a screen with slots dimensioned to pass the fibers while capturing the ink particles and using centrifugal cleaners which remove the ink particles based on their higher specific gravity. A problem with the agglomeration method is that the agglomerated ink particles are often not of uniform size so that a portion of the particles are sufficiently small to pass through the screen and the centrifugal cleaners. These particles eventually end up contaminating the paper made from the recycled pulp, and producing paper having a high speck content, a low brightness, or an unwanted shade of color. This problem is particularly evident with papers printed with inks which do not agglomerate well and which produce more smaller or finer particles which may escape the screens and cleaners.
It is therefore an object of the present invention to provide a method for making pulp produced using secondary fiber originating from recycled printed paper.
It is another object of the invention to provide a method for separating ink from printed recycled paper by agglomeration of ink particles released from paper in the repulping process.
Yet another object of the invention is to provide an improved agglomeration deinking process for use in recycling printed paper.
Another object of the invention is to provide an improved agglomeration deinking process which is effective in removing fine ink particles which may escape the standard separation stages.
Still another object of the present invention is to provide a method for producing brighter papers prepared from recycled papers printed with various inks.
An additional object of the invention is to provide an improved agglomeration deinking process and associated apparatus which is relatively simple to use.